The present invention relates to a wireless communication system. In detail, the present invention relates to a method and apparatus for acquiring system information by a terminal in a wireless communication system, the method comprising the steps of: acquiring time and frequency synchronization from a synchronization channel; performing PBCH detection in a wireless frame on the basis of the time and frequency synchronization; and acquiring the system information from the PBCH, wherein, when the terminal is a non-MTC terminal, the PBCH detection is performed by a singular sub frame in the wireless frame, and when the terminal is an MTC terminal, the PBCH detection is performed by a plurality of sub frames in the wireless frame.